Laser machining chamfered features in glass or glass-like articles such as sapphire, ceramic or glass ceramics is desirable because adding a chamfer to an edge makes the edge safer, in the sense that it is less likely to cause cuts or scratches when handled, makes it less likely to chip or crack and in general, makes the edge stronger. While chamfered edges are desirable, no methods exist for creating an article with a chamfered edge in one manufacturing operation. Prior art methods of producing chamfered edges involve creating a feature such as a through cut or trench in one operation and then producing a chamfer in one or more additional steps.
A chamfer is a bevel created on an edge formed by two adjoining surfaces. These surfaces typically are at approximately right angles at the edge where they adjoin, although other angles are possible. FIG. 1 shows a schematic cross-section of an article 10 produced without a chamfer. In this case the sides 24, 26 have been formed by machining the article from the top surface 20 to the bottom surface 22. Note the edges 12, 14, 16 and 18 where the top surface 20 and the bottom surface 22 adjoin the sides 24, 26. FIG. 2 shows the same article 10 except with chamfers 32, 34 applied to the edges where the top surface 20 adjoins the sides 24, 26. Note that chamfers could also be applied to the edges 18, 16 where the bottom surface 22 adjoins the sides 24, 26 in the place of or in addition to the top surface chamfers 32, 34. In addition to straight beveled chamfers as shown in FIG. 2, rounded chamfers are sometimes desirable. FIG. 3 shows the same article 10 with rounded chamfers 52, 54 where the top surface 20 adjoins the sides 24, 26.
Glass cutting has been traditionally realized by a mechanical saw approach, which scribes the glass and follows this step with a mechanical breaking process step. In recent years, laser technology has been adopted for glass cutting, which typically employs a laser as a localized heating source, sometimes accompanied by a cooling nozzle, to generate stress and microcracks along the trajectories described by the passage of the laser beam to cut the glass. Such resultant stress and microcracks may either be sufficient to cause the glass to fracture and separate along the designed trajectories or may require a follow-up breaking step to separate the glass. Existing technologies utilizing a laser only without the match of a cooling source include MLBA (Multiple Laser Beam Absorption) cutting technology as described in US patent applications 2007/0039932 Device for Separative Machining of Components made Form Brittle Material With Stress-Free Component Mounting and 2007/0170162 Method and Device for Cutting Through Semiconductor Materials, which use a near infrared (IR) laser source in combination with a pair of reflective mirrors to maximize the volume absorption of photon energy in the glass along the path to be separated so that there will be sufficient thermal stress generated so as to break the parts without needing to apply additional force. This technology, however, does require an initial mechanical notch to function as a pre-crack. The laser generated stress will make the initial crack propagate to form the separation. Another method of cutting glass or other brittle material is described in U.S. Pat. No. 5,609,284 Method of Splitting Non-Metallic Materials, which uses a CO2 source to heat the glass following with a cooling nozzle to generate stress so as to initiate microcracks along the cutting path, and then applying a mechanical breaking step to separate the glass. None of these methods address forming a chamfer on the resulting edges.
Laser machining of glass and glass-like articles can be performed for the purpose of machining shapes into the surface, for instance machining depressions to hold liquids, or machining thru holes for applying controls such as push buttons to the article or to provide a via to pass electrical signals, fluid or light through the article. U.S. Pat. No. 6,143,382 Glass Substrate Having Fine Holes describes a method of drilling fine holes in glass but this method requires doping the glass with silver atoms to promote absorption of the laser energy. Another U.S. Pat. No. 6,756,563 System and Method for Forming Holes in Substrates Containing Glass, describes a method of forming holes in glass substrates. Neither of these approaches discusses forming a chamfer on the finished hole. US patent application 2006/0127640 Glass Substrate With Fine Holes And Method For Producing The Same discusses drilling holes in a glass substrate with a laser and subsequently using a wet etch with strong acid to form rounded edges on the holes, but this involves adding one or more operations which add additional operations and equipment to the manufacturing process. This prior art illustrates the difficulty in creating chamfers on features internal to the article, such as holes or other openings machined into the article. Chamfering these edges often requires specialized equipment and fixturing in addition to requiring additional manufacturing steps.
U.S. Pat. No. 6,521,862 Apparatus and Method for Improving Chamfer Quality of Disk Edge Surfaces With Laser Treatment describes a method for producing smooth chamfers on a glass disk by mechanically grinding the chamfers and then melting them slightly with a laser. This produces smooth chamfers but requires at least two extra manufacturing operations and at least two separate machines to achieve a chamfer of acceptable quality.
What is needed then is a method and apparatus for forming features in glass or glass-like articles which can form high quality beveled or curved chamfers on both external and internal laser cut edges in one manufacturing operation.